STUDIES OF THE MACBOCHIEES. 
371 
different is it ! Quite as different, we may say in truth, as are 
the humeri of these birds. 
The tensor patagii longus in Ghcetura pelagica has the usual 
origin and insertion that it has in so many of the Class. 
Cypseli and Trochili both possess all three pectoral muscles , 
but in such a form as Micropus they are none of them unduly 
developed ; better so in Chcetura ; while in the Trochili they are, 
comparatively speaking, enormously developed. 
Owing to the entirely different shape of the humerus in Swifts 
and Humming-birds, the tendons of the pectorals make 
dissimilar insertions. For instance, the pectoralis major in 
Micropus is inserted upon the entire palmar aspect of the large 
hook-like radial crest of the humerus of that Swift ; but Trochilus 
possessing no such process upon its humerus, the muscle is 
obliged to insert itself more or less upon the body of the bone, 
at a point which would be considered as the base, upon the 
palmar side of a radial process did such a thiug exist there. 
How the pectoralis secundus in Micropus is inserted at the 
head of the humerus upon its ancoual side, between the summit 
and radial crest or hook ; while in the Hummiug-bird this second 
pectoral sends its tendon across the head of the bone, to be 
inserted at the distal margin of the pneumatic fossa. The 
insertion of the third pectoral in these two grorrps of birds is 
more similar. 
So here, again, we see that Swifts and Humming-birds are 
markedly different with respect to another class of muscles which 
make up, in part, the fundamental organization of their wing- 
structures. 
Among the essential characters of the wing we still have left 
the skeleton, but I have already published my views and drawings 
in regard to that part of their economy elsewhere (Proc. Zool. 
Soc. 1885 and 1887). I have there shown conclusively that 
the humeri of Swifts and Humming-birds are very differently 
formed bones indeed, and the reader has but to refer to the 
figures in the papers to which I allude to be convinced upon 
this point. 
As I have elsewhere stated, the humerus in Micropus is a 
non-pneumatic bone as in the Swallows ; while all Humming-birds, 
so far as I have examined, have pneumatic humeri. Still 
my statement Proc. (Zool. Soc. 1887, p. 503) requires some 
modification, for since that was written I have found that the 
